Electrical insulating material



Patented Apr. 14, 1942 ELECTRICAL INSULATING MATERIAL Thomas Robertson Scott and Archibald Alan New,

London, England, assignors to Interna tional Standard Electric Corporation, New

York, N. Y.

No Drawing. Application December 20, 1938, Se-

rial No. 246,827. 24, 1937 1 Claim.

This invention relates to electrical insulating materials, and particularly to insulating materials for use in electrical condensers, e. g. high frequency condensers, an object being to produce an insulating material of high specific inductive scapacity (hereinafter referred to as permittivity), and low dielectric angle of loss (hereinafter referred to as power factor).

It is well known that many hydrocarbon polymers particularly vinyl compounds have satisfactory electrical properties, e. g. satisfactory dielectric breakdown strength low power factor and so on; such materials are also flexible or are capable of being rendered flexible, and polystyrene may be mentioned as a well-known example of such a material. On the other hand, pure polymerised materials such as polystyrene are not in general suitable for use in condensers in view of their low permittivity, and in view of the fact that their softening point is in general relatively 10w.

According to the present invention there is provided an insulating material comprising polymerised material in which are embedded finely comminuted inorganic particles, selected in order to produce an insulating material having a permittivity at least 10% greater than that of the original polymerized material without raising the power factor of the resulting insulating In Great Britain December material may be an aromatic mono-olefine such as polystyrene, or an aliphatic olefine such as polyisobutylene or poly-ethylene. Alternatively a mixture of polymers may be employed, e. g. polystyrene blended with polyisobutylene or polyethylene, as described in our British Patent No. 507,323. Fillers and plasticisers may be added as desired, provided that the permittivity, power factor and other properties of the resulting insulating material .are not thereby unduly impaired. For example, the polymerised material such as polystyrene may be blended with rubber or the like, with or without the addition of rubber plasticisers such as a ceresin wax, in accordance with British Patent No. 357,624. Alternatively the polystyrene may be blended with a plasticiser in accordance with United States application, Serial No. 190,032, filed February 11, 1938 and assigned to the present assignee.

The finely comminuted inorganic particles may be of crystalline form, whether in two dimensions such as mica, or three dimensions such as marble, Iceland spar or load chloride.

Particulars are given in the following table 5 of results obtained by admixing various proportions of mica, Iceland spar, commercial rutile and load chloride with a mixture consisting of 63% polystyrene, 30% rubber and 7% ceresin wax (i. e. a mixture'according to British Patent material above 0.0025. The original polymerised 30 No. 357,624)

Material A B C- l) E F G 11 Percent Percent Percent Perrent Polystyrene-rubber P 1 st renc-rubber-l mica 2.0 19.1 7.5 o y y 21.8 9.1 (H 24.4 10.0 18.2 33.9 15.0 13.8 35.8 16.7 12.0 42.0 20.0 17.4

Polystyrcne-rubber-i-lceland spar 2.71 8.9 3.5 18.0 7. 5 l3. 1 $16 9.1 23.1 10.0 17.8 32.3 15.0 29.8 40.3 Z10 46.6

Polystyrcne-rubber-l-commercialrutile 4.17 17.0 4.7 (C(allqc.) 3.29 .0016 +6.67 19.6 27.3 8.6 3.46 25.3 30.2 9.4 3.88 .00l8 --2().0 41.1 40. 7 14.0 4. 40 .0020 +33. 3 I 60.0 Polystyrenc-rubber-Head chloride 5.85 39.4 10.0 (c6130.) 3.86 .0009 -40.0 40.4 50.5 15.5 4.4 .0010 -29.0 60.5

of loading material-by weight. of loading material-by volume.

D shows dielectric constant of loading material. E shows dielectric constant of mixture-measur F shows power factor of mixtu G shows percentage increase B shows percentage re. of power factor. increase of dielectric constant.

The following table gives the results obtained by admixing various proportions of mica, Iceland spar, calc. spar, commercial rutile and lead chlowell-known roll type condensers, or the insulatin: material may be shaped into moulded plates or the like. The electrodes may take the form of ride with pure polystyrene. metal foil pressed into intimate contact with the Material A B D 1: r G

Polystyrene"... 2.5 .0003

Percent Percent Percent Polystyreno-l-mica 2.9 13 6.0 0.0 2.77 10.0 21 11.3 17a 11.2 35.0 10.1 3.20 .0000 28.1

Polystyrene+lecland spar 2. 71 3 5.6 8.2 2.86 .0008 10.0

Polystyrene+calc. spar 2.71 13 5.6 8.2 2.82 .0004 12.8

(Cale) Poiystyrene+commercial rutile 4.17 13 3.7 (14) 3.00 16.2

1 d hl d 35 as 2 0 'ki 'ls) 4 04 0007 41 0 Flat ne cacorie I the invention.

' Pcrmillivity Silver chloride l1. 2 Pure rutile 120-130 Zircon (Z1 Si04) 12 Cassiterite (S1102).

Pyromorphitc Calomel 14 Colundum l2 Cerrussite (PbCO;) 24 Lead chloride. 42 Rochelle salt. 80 PbO 25. 9 CuO 18. 1

Power factor Aluminum oxide sintercd at l7301750 C.

8. 3 Quartz or fused silica 5.0 .0002 Commercial stcatite materials (forms of magnesium silicate) known under the trade name Alsimag as the products of the American Land Corporation 0. 196 6.0 .0006 Nov 197 6.0 .0012 N0. 5.8 .0003 (Mainly rutile) No. 192 85 .0008 Ultra steatitc (a form of magnesium silicate),

product of the General Ceramics Co 6. 3 .0007 Commercial titanium dioxide fired twice at Insulating materials in accordance with the invention may be applied in the manufacture of condensers as flexible films for winding into the insulating material, or metal may be sprayed or deposited onto the surface or surfaces thereof.

Preferably not more than 25% by volume of finely comminuted inorganic particles will be added to the polymerised material, and furthermore it is desirable that the added particles should have a permittivity value of 6 or above.

In preparing insulating material according to the invention, polymerised material may be dissolved in a suitable solvent, e. g. benzene, to form a thick dope to which the finely comminuted particles are added; thereafter the resulting mixtures may be sprayed or cast in a manner well known in the art in the preparation of films.

particles may be milled into the polymerised material in a manner similar to that employed in the rubber industry for incorporating fillers in rubber.

What is claimed is: An insulating material for use as a dielectric of a condenser comprising a binding agent primarily consisting of polymerised styrene and an admixture of powdered particles of lead chloride, embedded in said binding agent in an amount not exceeding 25% by volume and not suflicient to raise the power factor of the resulting material above .0025, but sufiicient to raise the permittivity of the resulting material by at least 10%. THOMAS ROBERTSON SCOTT. ARCHIBALD ALAN NEW.

Alternatively, the finely comminuted inorganic 

